Shuichi Akai and Rei Furuya
Since joining the Black Organization, Rei has always considered Shuichi as a worthy rival, he wants to compare his capacity with Shuichi and thinks he is the only one who could defeat Shuichi. Shuichi always shows respect towards Rei, he admits Rei's capability and feels interest everytime he faces Rei, he also makes Rei feel quite confused sometimes. Their relationship is becoming more bitter and dramatic when Rei misunderstood Shuichi killed his best friend - Scotch, but actually the one who indirectly caused Scotch to die was Rei himself. Shuichi chooses to keep a secret, continues to let Rei misunderstand him instead of letting Rei know that painful truth. Over time, Shuichi appears to help and protect Rei in some cases, he gradually wants to compensate for the losses which Rei has experienced, he also reveals that he doesn't want to be Rei's enemy. For now, Rei is temporarily lowering his hatred to working well with Shuichi and Conan in destroying the Black Organization.
In the Unfriendly Girls Band case, the flashback shows that during the time of infiltating Black Organization, Shuichi and Rei often go on missions together, sometimes with the cooperation of Rei's best friend - Scotch, they always bring guitars for relaxation while on duty.
In the Betrayal's Stage case, the flashback continues to reveal Rei's resentment for Shuichi. That is when Scoth's real identity as a police officer was discovered by Shuichi, led to suicidal thoughts, Shuichi convinced him not to, but suddenly heard Rei's approaching footsteps, believed the organization's members were coming, he chose to commit suicide, destroyed his cellphone to protect his identity as well as his family and friends. Not letting Rei find out that himself was the one who indirectly caused his best friend's death, Shuichi lies that he was the one who ended Scotch, "The traitor must be punished". This event became a cut in Rei's heart, and Shuichi deliberately takes the blame which didn't cause by him, wants Rei to never forgive him rather than lets Rei know that cruel truth.
After Shuichi's true identity as an FBI agent had been ferreted out, he was hunted everywhere by the organization. Having cherished thoughts about Shuichi for a long time, Rei felt very interesting and looking forward to defeating Shuichi in a fierce battle. However, Shuichi was killed by Hidemi in the Clash of Red and Black case, which made Rei unsatisfied and believing that only he could beat Shuichi. With the question "Is Shuichi really dead or not?", Rei plans to disguise as Shuichi to find the truth.
By the makeup skill of Vermouth, Rei approaches Shuichi's friends under the figure of him and observes their reactions, even teases teammates from the Black Organization. Through the surveys at Teito Bank, Beika Department Store, Mori Detective Agency and Bell Tree Express, Rei temporarily belives that Shuichi is dead, he and Vermouth decided to not impersonate Shuichi anymore. But, in this whole process, Rei didn't know that the real Shuichi, who is being in a fake identity as Subaru Okiya had also noticed his impersonation and was amused by it.
When Conan was kidnapped in the Detectives' Nocturne case, Subaru instantly chased after the car which containing the kid. When arrival, he was about to take action but saw that Rei and Masumi were also here, so he stood outside the game to let them rescue Conan by their own way, Rei also noticed Subaru's leaving car. While befriending the Mori family, Rei secretly used their computer in the Cabin Trap case, but the machine was hacked by Subaru and deleted all data. Although Rei promptly copied them, he still wondered who did it. At Kudo house, Subaru smiles in front of a computer while sipping a glass of bourbon.
In the Delivery Service case, although they work separately, the actions of Subaru and Rei contribute to helping the Detective Boys get rid of the truck containing a corpse. At the end of the case, Subaru observes Rei from Kudo house window, while Rei also notices the house and the person inside. Continuing to come near Shuichi's friends in the Cherry Blossom Shrine case by the disguise as Tohei, Rei detects important information about Shuichi's fate and tells Vermouth that he will make a plan to unearth the "surprising inside story".
In the Scarlet Showdown case, Rei prepared everything to expose Shuichi's fake death, he pretends to be a delivery and comes to Kudo house to approach Subaru. After saying implied words like this is not the first time they met each other, Rei immediately gets into the main topic, informs Subaru that his friends - Jodie and Camel are in danger, so if he want them to be safe, he must remove the mask and tell the truth that he is Shuichi. Following Rei's words, Subaru removes his medical mask, but it shows a normal face. Rei is awkward and says it's not the "mask" he means, he asks Subaru to take off this fake face and reveal Shuichi's real face. Subaru seems to not understand what is Rei saying, which leads Rei to personally searches the voice changer on his neck, but finds nothing.
While Rei queries Subaru, the real Shuichi appears in Jodie and Camel's car to rescues his friend from Rei's allies by shooting at their tires. After compromising with Rei's allies, Shuichi borrows their phone and talks to Rei, he reveals Rei's true identity as a police officer, and deduces that Rei want to use Shuichi's capture to get a higher position in the Black Organization. Shuichi sympathizes that Rei wants to build his trust in order to get deep into the heart of that organization and capture the boss, but he thinks Rei has applied the wrong way. Shuichi reminds Rei that although they are on different front lines, they are both considered powerful allies, sharing a same goal, so don't just focus on the old resentment and lose sight of the real prey. Before ending the conversation, Shuichi also admits he never wanting to see Rei as his enemy and emphasizes that he still regrets about Scotch's incident. After hearing Shuichi's advice, Rei's heart is tightened again, he apologizes Subaru for getting the wrong person and leaves with his allies.
In the Betrayal's Stage case, Rei went to musicial theater to investigate Asaka's whereabouts, he ran into Subaru and excitedly greeted the acquaintance. Although they both pretended to be huge fans of singer Rokumichi and happily chatted about his songs, deep inside, they actually knew each other's intentions. After unexpectedly witnessing the dead body of Rokumichi, the two solve the case together in a very good way. However, during the investigation, they were quite distracted because memories of Scotch kept popping up. Their behavior annoyed Vermouth, she urges Rei to quickly clear the case instead of keep staring at Subaru. Rei also assumes that this Subaru is left-handed, not the same Subaru he met last time. When Subaru questions about Rei's interest in his dominant hand, Rei says nothing but emphasizes that there is a right-handed man he very wants to take down. At the end of the case, Rei says he desires to pull down Subaru's collar but will save it for another day.
In the Lost Phone Strap case, Rei informs that recently, he is often sleepy everytimes he drives near Kudo house, so he parks here to take a nap. Although Subaru considers it makes senses, he knows that Rei is intentional tracking his movements. Subaru then asks Rei to take the Detective Boys on his behalf to find Ai's phone strap, but that's fine if Rei has another reason not to leave. Rei replies that although he really hasn't wanted to leave this place yet, he willing to help the kids. When Agasa asks if they can find the small item in a sea of people, Subaru says he can be assured because the case involved two of Japan's best investigators.
Rei also shares some interactions with Shuichi's relatives, such as hunting Shiho, refusing to admit that he had met Masumi 4 years ago. Especially in the Black Bunny Club case, it shows that Rei had a close contact with Elena and Miyano when he was a child, as well as revealing he is a half-breed like Shuichi. Nine hours after the case, Rei infiltrates Kudo house and is confronted by Shuichi. The two point guns at each other, Rei arrogantly smiles at Shuichi and says he was so careless, Shuichi replies that he not because he actually knew Rei would be here today. Their conversation is getting very stimulating but suddenly interrupted by the appearance of Yusaku and Yukiko, who invite Rei to sit down and have some tea.
The content of that talk has not yet been revealed. Only knowing that after the night, Rei's mood was more stable, perhaps he agreed to put his grudge aside to work with Shuichi and Kudo family to smoothly overthrow the Black Organization. As for Shuichi, he is busy handling the FBI Serial Murder case, so he temporarily don’t liaise with Rei, who then clashed again with Kid, just like the way Shuichi did.
In the Darkest Nightmare case, the real identities of Rei and other undercover agents were all found out by Curaçao through files theft. He chases her down to protect his identity, Shuichi also joins although Rei refuses the help. As a result of the pursuit, Curaçao's car is shot by Shuichi, plunged under the bridge and exploded, however, the girl runs away. Before disappearing, Curaçao timely sent a message named all the spies in the organization, caused Rei and Hidemi to be tied up and interrogated by Gin. Just as Gin is about to kill Rei, Shuichi shoots at a lamp, creates darkness and helps Rei to take an chance to escape.
Knowing Curaçao's whereabouts, Rei and Shuichi go to Tohto Aquarium to capture her. The two negotiate on the top of a ferris wheel, Rei opposes Shuichi to send her to FBI, he wants to personally take her to Public Security Bureau. When Shuichi don't agree, Rei askes about the reason he saved him before, was it sincere care or just an act to force Rei give in to him at this time. Shuichi dodges the answer, makes Rei feel so impatient, he quickly rushes into Shuichi and uses martial arts to decide who can take Curaçao away. A very intense battle is going on, they're rolling together on the ferris wheel under a splendid fireworks sky, then fall to the control area inside the ferris wheel, where they continue to compete until Conan stops them and informs that the organization has planted bombs here. In order to deal with the bombs, Shuichi lends Rei his bomb disposal equipment and assigns that he must successfully defuse them, which makes Rei mutters "It's easy to say".
While Rei is busy with his duty, Shuichi and Conan go out to observe the organization's movements and prevent them from rescuing Curaçao. Discovering that Rei has neutralized most of the bombs and Curaçao has no intention of returning to the organization, Gin becomes enraged and orders his teammates to shoot down the ferris wheel. The trio works together to protect the innocent from Gin's cruelty. Rei throws the remaining bombs into the sky to give Conan a chance to see Gin's helicopter clearly, the boy kicks a "miracle ball" that hits the helicopter and creates fireworks. The huge light helps Shuichi to distinctly see the rotor of the helicopter and straightly fires a bullet into it, causes Gin's team heavy losses.
Before fleeing, Gin intentionally caused the ferris wheel to roll towards the aquarium, Rei fastly throws Conan over to Shuichi, lets the boy can approach it. With the silent sacrifice from Curaçao, Conan succeeds in making the ferris wheel to stop, prevents it from taking the life of a thousand people in the aquarium. Both Shuichi and Rei breathe a sigh of relief at Conan's courage. At the end of the case, the two look at each other with nostalgia, have something to say but chose to leave, wait for another chance to meet again. Also with Conan's arrangement, Rei and Hidemi are cleared of suspicion and allowed to work normally in the organization.
In other cases, the two are also considered to be somewhat related. For example, in the Zero the Enforcer case, Rei says that there is a person who he very afraid of, implying Shuichi or Conan or Kuroda. In the Scarlet Bullet case, Rei will surely be the first one to get mad when he learns that a whole stadium of his beloved Japan was shatterly destroyed just because of the FBI. And in Zero's Tea Time story, it shows that Rei still often drives around Shuichi's place and mutters that he will never forget what Shuichi did to him.
In a 2019 interview, author Gosho Aoyama said that the purpose he created Rei was to balance with Shuichi. Rei is good at anything, but everytime he confronts Shuichi, he always loses his temper and can't defeat him. Shuichi is not only Rei's weak point but also the unique one who can make Rei confused, this makes the fans feel very amused. And they got even more excited when discovers that in a 2016 interview that Aoyama also said he was the one who had suggested the producer to add the scene which Shuichi and Rei fought on the ferris wheel into Movie 20, because he wanted audience to enjoy their exciting relationship.
With the enthusiasm that Aoyama has invested in the story of Shuichi and Rei, the fans really respect him and give nickname "Lovely Ship Captain" to him. Along with the golden age of the Internet, Shuichi and Rei's plot gradually became very popular, in just a short time, the keyword "AkaiAmuro" became a hot search on so many social networking platforms in Japan and even other countries. To this day, the total number of fictional artworks/comics about the two on Pixiv has reached more than 21700 produces. They also stand in high positions in the favorite anime characters ranking.
Coincidentally, both of them are half-breed and also have three names, first is codename Rye and Bourbon when working in the Black Organization, second is fake name Okiya Subaru and Amuro Tooru when infiltrating Conan's life, third is birth name Shuichi Akai and Rei Furuya. Even more, there is an event called Forgiven held every year, where many artists will share countless beautiful drawings of the two for everyone to admire. Forgiven is the name of a blend alcohol of rye and bourbon, in addition, it also represents the wish that one day Rei will forgive to the one who don't want to be forgiven - Shuichi.
Another interesting thing is that although their real names are Shuichi and Rei, their surnames Akai and Amuro are more commonly used by the general public.
Fans have come up with many good theories about Shuichi and Rei's future. Some people say Shuichi is very noble, the way he took all the blame on himself was really saved Rei a lot. Because all of Rei's close friends died, left him behind, if Rei knew one of those friends was indirectly made to die by him, how much more painful would he be? When Shuichi chose to hide the truth, he accidentally stepped closer to Rei's world and created an axiom that: he will replace those best friends to keep an eye on Rei from now on. So then, the more Rei hates, the more Shuichi seeks to protect him, silently helps him and ready to compensate the hurt which Rei had experienced.
Many others think that Shuichi and Rei intensely interact with each other was not solely due to Scotch's death, emphasize that this factor is just a part. Because in the first place, when the two first joined the organization, they always worked together and wanted to compete with each other. These fans say the "sacrifice" is a risky thing which can happen while spying, the one who works in the security industry has to accept it. Rei himself is an adult, elite and brave policeman, then he can't lose his mind to the point of clinging the past for so many years like this. So, it can be seen that in their relationship, it's not only Shuichi takes the initiative, but also Rei has followed Shuichi for so many years just to be able to confront Shuichi, and the reason about Scotch is one of the excuses.
This inference does not deny that Scoth is the cause of climax in their relationship, it just emphasizes that if some one thinks Shuichi and Rei's whole relationship is made by Scoth's sacrifice is completely inaccurate. The first connection between them is because they want to compete with each other. Assuming Scoth doesn't die, Rei will still find a way to approach, companion and tighten up with Shuichi. The key starting point in their relationship is like that. People also praise that author Aoyama is very profound when he wrote such a dramatic story for Shuichi and Rei, tightened them into a bitter relationship, which make fans feel heartbreaking too.
And with Detective Conan's criteria, "there is always only one truth", so maybe one day the author will let everything be cleared. Many fans say they don't dare to imagine the scene which Rei knows the truth, they hope Shuichi will be there to comfort and soothe Rei's hurt. Even if Rei bursts into tears, Shuichi will let Rei cry on his shoulder. Others think that, with Shuichi's personality, he will find a way to let the truth be buried forever, maybe he will choose to take the enemy's bullet for Rei in the final battle, and Rei will gradually forgive Shuichi by taking care of his wound. No matter what happens, everyone expect they will resolve the misunderstanding, have a good ending and will become each other's soulmate, finally, after defeating the Black Organization, they will take each other on a trip, leaving this suffering world behind.
Noting the chapters/episodes which Shuichi and Rei appear together or related to each other.